Posted
by
chrisd
on Sunday January 12, 2003 @10:38PM
from the virtual-classes-for-the-universe dept.

Microsofts slave writes "Scientists belive that they have found the earliest objects (new zork times registration required) in space. 26 galaxies and three quasars were observed at thirteen billion light years away, at time when the universe is belived to have been only 1 billion years old."

Depends on your definition of "death". Most scientists agree that the universe will never contract (although some disagree, which is okay, because when it comes down to it, we won't be around if the latter happens, and if the former happens, well, who knows), but will just keep expanding. I wonder if there's enough matter to fill an infinite universe.

Also, if our universe that we know started out as a black hole (someone posted some formulas and stuff in another thread), wouldn't it be safe to surmise that all black holes create a new universe?

"Scientists belive that they have found the earliest objects (new zork times registration required) in space. 26 galaxies and three quasars were observed at thirteen billion light years away, at time when the universe is belived to have been only 1 billion years old."

If so, that means the average rate of expansion of the universe since that time had to be at least 4/5 C... Unless our physics model is flawed on the large scale, whish it probably is... Who knows, maybe the observed outward acceleration of the universe is due to a force many orders of magnitude weaker than gravity but repelling and inversely proportional to R instead of R^2 so it would be important on the extremely large scale but unnoticeable on the scale of individual galaxies... That would fubar all our redshift measurements and wreak havoc on our largely speculative cosmological model... who knows...

If so, that means the average rate of expansion of the universe since that time had to be at least 4/5 C

I believe the current belief is that the "other side" is heading away already beyond C. We will never see that stuff and there is no way that a Dr. Evil on that side can catch us (under current phyz.) Perhaps this is the anthropic principle protecting us.

(The anthropic principle is cool. I always wanted to start a cult around it -- a more logical El Ron:-)

I meant 4/5 C reletive to the epicenter of the Big Bang, if there is one. Speaking of which, shouldn't it be obvious from the distribution of all the objects that are that distant which direction it is to the epicenter of the big bang?

There is no epicenter of the Big Bang. It's everywhere. Space itself was created with the Big Bang, remember.

Imagine the universe as a balloon that starts out incredibly tiny, and is then blown up to full size. What's the epicenter of the balloon? It doesn't have one, it's everywhere.

This is also why it's possible that two galaxies can seem to move at higher than c relative to each other - they do not actually move that fast, rather the space between them can expand to make it seem that way.

Note: I meant the *surface* of the balloon. The sphere has no center. And you can draw two points on the balloon, and watch them move apart as the balloon expands, even though they do not move on the surface.

If everything started with a Big Bang [nasa.gov] from a singularity roughly 10-20 billion years ago, how is it that things came to be physcially 13 billion or more light years apart? I understand that the "Doppler" redshift is caused by great speed away from us. But is the universe seriously expanding at anything near lightspeed?

Some suggest [berkeley.edu] that initial expansion was faster than light speed, and that the Hubble expansion is accelerating.

But is the universe seriously expanding at anything near lightspeed?
The universe seems to be open, which means it's infinite in extent. However, we can only observe a finite part of it, because light from more distant parts hasn't had time to get to us since the Big Bang. Stuff very far away from us, beyond what's observable to us, is theoretically moving at greater than the speed of light relative to us.

IIRC, in standard cosmological models the stuff at the edge of the observable universe is moving away from us at exactly the speed of light.

You can also think of the expansion as a growth of space itself, not just the motion of galaxies away from each other.

While what you say may be true (or not), it does
not seem to be a requirement. If we can see 13
billion light years, and there is only another
billion to go, it seems quite possible that we
could see nearly the entire universe, as it existed at
the age of 1 billion.

Of course it was all dark, since the plasma hadn't
allowed neutral hydrogen to form yet.

There are parts of the universe that are receding from us at the speed of light and faster. Although we might choose a definition of "universe" such that things permanently outside our light cone are excluded, we can indeed see all the way to the big bang -- that's what the cosmic microwave background is.

So we can see all the way back to when the universe was small. It would appear that the further back you look, the more of the universe you can see.

We can see 100% of the time, but not 100% of the space. We can see how the Big Bang looked, but only in the region of space that's observable to us. Yes, our observable region will expand, but if the universe is open, it will never include the whole universe: it'll always be a finite volume of space, whereas the volume of the universe is infinite.

Although we might choose a definition of "universe" such that things permanently outside our light cone are excluded
In a universe with zero cosmological constant, there is nothing that is permanently outside our observable region.

How do you know / suspect this? I'm not suggesting that you're wrong, I'm just wondering what the evidence to support it is. After all if its outside of the observable universe, how can we tell what features it has?

General relativity allows two types of solutions for a homogeneous and isotropic universe, open and closed. The open version is infinite in volume and never recontracts. The closed version is finite in volume, and recontracts. Measurements of the cosmic microwave background and the cosmological constant show that we're living in an open universe.

After all if its outside of the observable universe, how can we tell what features it has?The observation that we live in an open universe, combined with general relativity, make a definite prediction: that the size of the part of the universe observable to us will grow without limit. It's infinite in the sense that if you wait long enough, you can see as much of a volume of space as you like. Sort of like how the number of integers is infinite in the sense that if you count long enough, you can name as many integers as you like.

Thanks for clearing that up. I can now see where you're coming from on the open universe angle.

One thing that still doesn't make sense though; If the observable universe will grow without limit then the distance that we can see further back in time will also grow without limit - isn't this a contradiction with the claim that that time started at a finite distance in the past?

If the observable universe will grow without limit then the distance that we can see further back in time will also grow without limit - isn't this a contradiction with the claim that that time started at a finite distance in the past?No. If the universe's age is X, then X is how far back in the past you can see. X increases by one year with every year that passes.

No. If the universe's age is X, then X is how far back in the past you can see. X increases by one year with every year that passes.
Ah good point. I hadn't considered that. But then, if the universe has grown to infinite size in finite time doesn't that imply an infinite rate of expansion?

Interesting stuff. Have you got some links with some more indepth explanations. One thing that I still have a problem with is how can it be expanding if its already infinite - infinity is just an uncontrolled or divergent growth process. How can such a process be growing in size? Or to put it another way, at the time it was a singularity it must have been finite in size, so it must have had a period of expansion that was infinite in rate. If not how could it have been an infinitely sized, yet singular point?

I'd suggest starting with Relativity Simply Explained by Martin Gardner. After that, you might try a recent edition of an astronomy textbook. (So much new stuff has been learned about cosmology recently that even a 2000 textbook is probably too out of date.)

BTW, I wonder if Slashcode imposes a limit on the depth of replies to replies to replies...:-)

BTW, I wonder if Slashcode imposes a limit on the depth of replies to replies to replies...:-)
Well, there's only one way to find out...;)

I'm read a fair bit on relativity and string theory, I'm quite familiar with the ideas of inflation et al, I've just never come across the definite assumption that the universe is infinite in expanse. Are there any specific weblinks - yup, I'm that lazy, the library is in the next building, and its raining;)

The article is not about quasars. Quasars are sisters of a group of objects known as QSOs. QSOs and quasars are bright across 15 orders of magnitude of the light energy spectrum, but quasars are radio-bright and QSOs are not. There was no mention in the article of radio studies being performed in concert with the visible and infrared observations, so these objects are QSOs until further notice. And since the galaxies are only visible because of the stars in them, the article's title is partly correct.